1. Field of the Invention
This invention relates to polarimetry and ellipsometry. More particularly, it relates to a novel static polarimeter requiring less hardware while providing improved accuracy, and a smaller beam size.
2. Description of the Prior Art
T. Smith wrote an article entitled "An Automated Scanning Ellipsometer" in Surface Science 56, No. 1, 212-220 (June 1976) which shows an automated ellipsometer in FIG. 1 thereof with a polarized beam splitter 4 which supplies a fraction of the beam from the light source 1. The beam, which passes through the polarizer, is reflected from the surface of a sample. A portion of the reflected beam reaches a 45.degree. analyzer prism 6 and it is measured by a detector 8. Another portion of the reflected beam 7 reaches a second analyzer prism which splits the portion of the reflected beam it receives into parallel p and perpendicularly s polarized segments. There are detectors connected to receive the separate p and s segments. It should be noted that the prism 6 and the prism 7 are separate but juxtaposed. Accordingly, some of the light in the beam reflected from the surface of the sample S may not be received by any one of the three detectors 8, 9, and 10.
In addition, three detectors are used to measure the reflected beam rather than the two detectors required in our system. Furthermore, since the beam is split from side to side, the detectors are dependent upon the uniformity of the beam from side to side. Smith requires careful alignment of the beam.
The sources of error in Smith overcome by the present arrangement are (1) alignment of the beam; (2) uniformity of the beam, and (3) uniformity of the sample. In addition, the present arrangement permits focussing upon sample object surface areas as small as 1 mil.sup.2 whereas Smith cannot, since his error is on the order of a few mils.sup.2, Smith states that he requires uniform illumination (p. 219) and a large area (p. 213).
At page 220 of the Smith article under comments made at the conference where the article was presented, it is stated by M. J. Dignam "Rather than having two beams, we had in mind placing a reflected beam splitter with plates at normal incidence and then analyzing each of the beams with a polarizing splitter as you have done. The polarizing beam splitter is properly oriented to get all the information from a single beam. You still have the calibration problems and the calibration of the beam splitter but I think it can be done with a single beam". That arrangement would use four detectors at the output end in place of the three detectors of Smith and the two detectors employed here as we interpret that statement made by M. J. Dignam. The result is a more complex set of twice as many data outputs, and five detectors instead of three with the attendant disadvantages of more sources of error and cost of computation. The present system employs a novel technique, which permits use of only three detectors, whereas heretofore, it had been believed that four detectors would be required.